Production of modulated high-frequency oscillations



Jan. 16, 1923. v 4 1,442,147.

R A. HEISING. I 1 PRODUCTION OF MODULATED HIGH FREQUENCY OSCILLATIONS.

. ORIGINALHLED NOV; 17.1.1916.

In Van for: Raymond A. flw'sl 'nq.

Patented Jan. 16,1923.

UNITED STATES PATENT OFFICE.

RAYMOND A. HEISING, OF EAST ORANGE, NEW JERSEY {ASSIGNOR T0 WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PRODUCTION OF MODULATED HIGH-FREQUENCY OSCILLATIONS.

Application filed November 17, 1916, Serial No. 131,868. Renewed May 2 7, 1922. Serial No. 564,218.

To all whom it may concern:

Be it known that I, RAYMoNn A. HEI- snv'o, a citizen of the Unitedfitates, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Production of 'Modulated High-Frequency Oscillations, of which the following is a full, clear, concise, and exact description.

This invention relates to the production of high, frequency oscillations and more particularly to systems and methods for producing high frequency oscillations modulated in accordance with low frequency signals or control energy to be transmitted.

An obj'ect of-the invention isto provide a novel and efiicient oscillator of the vacuum tube type.

Another object of the invention is to provide a modulation system in which the modulation is effected by variably diverting, portions of the normal space current of a vacuum tube oscillator.

Another object of the invention is to provide a modulation system in whichsignals may vary the effective electro-motive force of the source of space current of a vacuum tube oscillator.

Still other objects of the invention relate to certain methods of modulation and circuit arrangements hereinafter described and particularly pointed out in the claims, the advantages of which will be apparent to those skilled in the art.

It has been found that the amplitude of the high frequency oscillations set up by an oscillation generator,such as the audion j tube oscillation generator of the type shown in U. S. )atent to Hartley No. 1,356,763, patented October 26, 1920, depends on the effective voltage supplied to the generator. Itis apparent then that, by varying this voltage supply in accordance With signals to be transmitted, the high frequency oscillations will be modulated in'accordance with these signals and maythen be im-, pressed upon any suitable transmitting apparatus. e i

To this end this invention embodies a generator of high frequency oscillations preferably consisting of avacuum tube of, the audion type connected to an oscillating circuit, and a means for varying the volt age supply of the generator in accordance with audio-frequency oscillations. The means for varying the voltage supply of the oscillation generator may consist of a vacuumtube of the audion type on whose input terminals the signals are impressed, the resultant amplified signals'in the output circuit being impressed on the output circuit of the oscillating tube, thereby making the high frequency oscillations have a speech signal wave form. These modulated oscillations may then be impressed on the transmitting terminals of suitable apparatus, such as a wireless antenna.

Such a meansfor impressing the low frequency oscillations on'the output terminals of an oscillating system is well adapted to systems in which the vacuum tube is oscillatingfreely, for in such a case it has been found that, by impressing the low frequency oscillations on the output circuit of such an oscillating tube in a manner hereinafter described, modulated oscillations of the desired form will result.- v

The invention is adapted for embodiment in systems of radio 'telegraphyand telephony and in high frequency wire signaling systems, and, in general, wherever areceiving device is rendered sensitive to signaling impulses or waves of low frequency by means of sustained electric or electromagnetic waves of high frequency transmitted from the sending station.

This invention will be set forth in the following detailed description'taken in connection Withthe accompanying drawing, in which Fig. 1 illustrates a, system of circuits embodying this invention in the case of a radio transmitting system; and Fig. 2 vrepresents a modification thereof.

Referring to Fig. 1 of the drawing, 1 is a vacuum tube, preferably of the audi in type, which contains a filament 2, a grid 3 and a plate 4. This tube, together with inductance 5 and capacities 6 and 32, acts as a generator of high frequency oscillations similar to the one disclosed in the Hartley Patent No. 1,356,763, wherein its action is described in detail. 7 is a sourceof negative potential for the input element or grid of said tube. Capacity 32 serves to separate the unidirectional current paths of sources 7 and 8' seats to enable plate 4 and grid 3 tov to the filament 2. Its output circuit includes ance with the low frequency wave a source of voltage 8 and a choke coil or autotransformer 9 whose function will be de scribed later. The oscillations in the output circuit of the vacuum tube, whose frequency is controlled by means of the variable condenser 6, are fed back into the input circuit by means of the inductive relation between coils 12 and 13, thereby insuring sustained high frequency oscillations. 15 is a modulating device, preferably of the audion type, which contains a filament 16, a grid 17 and a plate 18? said filament and plate, which form the output terminals for the tube, are shunted around the source 'of voltage 8, which serves as a source of current for the output circuits of both tubes. 20 is the battery for the input circuit 21 on whoseinput terminals low frequencyoscillations from a transmitter 22 are impressed by means of repeating coil 23. By some suitable means, shown here as a choke coil 9, the amplified low frequenc y oscillations in the output circuit 25 are impressed on the output circuit of the oscillating tube, thereby causing variations in the power supplied to the genera tor so as to give rise to high frequency oscillations modulated in amplitude inaccordform from source 22. The space current circuit of the oscillation generator is subject to the resultant electromotive force from both the source of voltage 8 and the choke coil 9. Hence we may consider them to be included in the power supply circuit of the generator. By means of transformer 26, the resultant modulated oscillations are impressed on the antenna 27.

The manner'in which the highfrequency oscillations in the ouput circuit of tube 1 are modulated-in accordance with the low frequency wave form may be explained as follows:

In the drawing, consider the part of the system containing the output circuits of both tubes. We may assume for explanation purposes that battery 8, choke coil 9 and the impedance between filament 2 and plate 4 constitute the main circuit, with the impedance between filament 16 and plate 18 acting as a resistance shunted around said battery and choke coil. This latter named resistance is not constant in value since the negative grid voltage of tube 15 undergoes variations according to the low frequency oscillations that are impressed on its input terminals. For illustration, consider} the instant at which the grid 17 has-beenmade more'nega-' tive by the impressed signals. tend to increase the impedance between fila ment 16 and plate 18, and so decrease the current flowing through the element 15 from battery 8. The choke coil will then have an electromotive force induced'in it, due to this This will constant so that more current will be sent through the part of the circuit containing.

filament 2 and plate 4 on account of the in crease of the impedance between the output electrodes of tube 15. In a like manner a decrease in the latter named impedance will produce a corresponding decrease in the current between'the output'electrodes of tube 1. Hence, variations in the current through the input circuit of. tube 15' will'produce a like variation inthe current of the output circuit of the tube 1; that is, the voltage supplied to the oscillation generator will be modulated accordance with the signal waveform impressed on the input circuit of the modulating tube.

In the preceding explanation it has been pointed out that the function of the tube-15 together with the coil 9 is to vary the effective unidirectional voltage applied to thetherefore the impedance of tube 15 and the.

portion of the constant current which it passes varies, the remaining portion of the constantcurrent which is the space current for tubel must also vary. -As the impedance of tube 15 increases the space current of tube 1 will increase, and as the impedance of tube 15 decreases the space current of tube 1 will decrease. Tube 15 therefore operates to modulate a direct current which is supplied to tube 1. Tube 1 producesoscillations vary.- ing in amplitude with the variations of this direct current supply. It will therefore be apparent that the modulating action differs from that in which high frequency oscil- 'lations are produced and later modulated.

element 9, although shown as a choke coil, may equally as well be considered as an auto-transformer'in which the primary and secondary windings are equal and united.

The operation of the system is the same in both cases. Fig. 2 illustratesa further modi-' fication of the system in which an ordinary transformer -9- having separate primary and secondary windings-30 and 31, respectively, has beensubstituted for the element 9. The

primary winding 30 is the output'circuit of tube 15; the secondary windingBl is in the output circuit of tube 1. 'Hence, trans former 9 serves as a means for impressing the amplified 10w frequency oscillations from the tube 15 on the' output circuit of tube 1 thereby giving rise to the desired In the above description of Fig. 1, the

modulated high frequency oscillations. The portion of the circuit of Fig. 2, not

shown but assumed to be located above the broken line ab may be identical with the portion of the circuit lying above the corresponding line w-b of Fig. 1.

This invention may be embodied 1n st1ll other forms without departing in any wise from the spirit of this invention the scope of which is defined in the appended claims. lVhat is claimed is: 1. An oscillation generator, a source of unidirectional voltage therefor, a variable impedance in series in a direct current circuit with said source of voltage, means for keeping the current from said source substantially constant, and means for varying said impedance in accordance with signals.

2. An oscillation generator comprising an electric discharge device" having a supply circuit, a source of voltage for said circuit, a variable resistance in series with said source, means for keeping the current from said source substantially constant, and means for varying said resistance in accordance with signals. 3. An oscillator comprising a vacuum tube having discharge electrodes, an input circuit and an output circuit, a constant current source of discharge current connected to said discharge electrodes and a variable impedance element directly connected to said sourcei to divert a portion of the space ourcordance with signals.

rent from said oscillator. a

4. A' vacuum tube oscillator having an asymmetric space currentcircuit including a unidirectional space current source, and a variable impedance element connected to points between which large difi'erence of potential exists in said space current circuit to divert a portion of the space current from said oscillator.

-5. A modulating system comprising avacuum tube oscillator having a space current circuit, a variable impedance device, and a source of substantially constant current for supplying a portion of said space current circuit, and said impedance device in parallel.

6. A modulating system comprising vacuum tube-oscillator having a space current circuit including a source of substantially constant current, a variable impedance element connected between two points in said space current circuit, and, means for varying the impedance of said element in ac- 7 The combination with a high frequency oscillator having a supply circuit, of a modulating device comprislng a vacuum electric discharge element having an input circuit and an output circuit, and electrodes terminating said output circuit within said element, a source of voltage for said supply circuit, the output electrodes of saidmodu blator being shunted around said source of voltage, means for keeping substantially constant the currentsupplied by said source, a source of low frequency signaling oscillations, means for impressing said low frequency oscillations on the input clrcilit of said modulator thereby modulating the voltage'in the supply circuit of said oscillator according to thelow frequency signals.

8. The combination with a high frequency oscillator having a supply circuit, of a mod ulator having an input circuit and an output circuit and electrodes therefor, a source of voltage and an inductance common to said output circuit and said supply circuit,

a source of low frequency oscillations, means for 1mpress1ng said low frequency,

oscillations on the input circuit of said modulator thereby producing amplified low frequency oscillations in its output circuit, said inductance serving as a means for'impressing said amplified low frequency oscilla-- tions on the supply circuit of said oscillator thereby producing modulated high. frequency oscillations, transmitting terminals, and means for impressing said modulated and a vacuum tube having an impedance varying element and an anode respectively connected to the opposite terminals of said first mentioned capacity element.-

10. An oscillator comprising a closed tuned circuit including a capacity element, a source of electrical energy, avacuum tube having a cathode and ananoderespectively connected to opposite terminals of said source, and conductive paths exclusive of said vacuum tube connecting the terminals ofsaid sourcewith the terminals ofasaid capacity element respectively. v

11. In combination, a tuned circuit including two capacity elements, a vacuum tube device having a'cathode, ananode, and a impedance varying element, said anode and said impedance varying element being connected to opposite terminals of one of said capacity elements, and said cathode being connected to both terminals of the other of said capacity elements.

- 12. In combination, a tuned circuit 111- cluding a capacity element, a vacuum tube device having a cathode, an anode, and an impedance varying element, said cathode being 'conductively connected to the opposite terminals of said capacity element through sources of electr cal energy oppositely oled with respect to said cathode.

13; n combination, a tuned circuit including a capacity element, an electron dishigh frequency oscillations upon said ter charge device having a cathode and two associated elements means connecting said associated elements to points of different potential in said tuned circuit, connections from said cathode to each terminal of said capacity element, and sources of current in each of said' cathode connections 'poledin such manner as to make one of said associated elements negative with respect to both said cathode and the otherassociated element. I

14. In combination, a plurality of discharge devices :each having an anode and a cathode, current supply means therefor, a circuit arrangement for said discharge devices, means including one of said discharge devices for'setting up oscillations in s aidcircuit arrangement, means to impress signals upon another of said devices and means for keeping'constant the sum of the anodecathode currents of said devices.

15. The method of controlling a vacuum tube oscillator'having an-internal asymmetricspacecurrent path.- which comprises variably diverting the normal space current from said path. ,1

16. The method of controlling the amplii tude of the oscillations produced by a vacuum tube oscillator having an asymmetricspace current path, which comprises shunting a portion of, the unidirectional current from said path and varying the amount of the current shunted.

17. Thegmethodof operating an electron discharge device having discharge electrodes, and an internal impedance control element wh ch comprises impressing an electronic tive force across the discharge electrodes of said device, varying the internal impedance of said device by-impressing a variable electromotive force between said impedance control element and one ofsaid discharge electrodes, and simultaneously variably shunting the space discharge path between the discharge electrodes of said discharge device to vary the current through the device.

18. The method of operating a vacuum discharge device which comprises supplying said device with continuous current from a constant current source, and variably diverting said' current frem said device.

19. The method of producing high frequency oscillations varying in amplitude in accordance With a control current which comprises deriving said control current from a constan'tcurrent source, and causing the remainder of current from said source to ,traverse the space discharge path of an electron discharge oscillator.

20. The method of controlling the amplitude of the oscillations produced by an elec. tron discharge device which comprises supplying said (18". ice with space current from a constant current source, and simultaneously absorbing in a variable impedance device a. portion of the energy of the current from circuit in energy feed back relation whereby said discharge device serves to generate oscillations, and means for variably shunting the internal space current path between said discharge electrodes to vary the space current supplied thereto.

22. A vacuum z'discharge device having dis- 1 charge electrodes, a constant current source connected to said electrodes to impress a unidirectional electromotive force therebetween, and means conductively connected to saidelectrodes for variably diilerting space discharge current from said device in accordance with signals.

23. A source of constant unidirectional current, anamplifier and an oscillator concurrent circuit, ,a constant current. source connected-in said space current circuit, and

nected to be supplied in parallel by said an impedance device of the order of magnitude of said discharge device connected I thereto for variably diverting space current from said discharge device.

25. An oscillator comprising an electron discharge device having coupled input and output circuits, a variable impedance path,

and a constant current source connected to supply current to-said device and said path in parallel.

26. In combination, two vacuum discharge devices, a constant current source, a circuit including two parallel paths in circuit with said source, each of said paths including the space discharge path of one of said vacuum discharge devices,.means for varying the impedance of one of said devices in accordance with control currents, and circuits associated with the other or said devices whereby it is 'caused to produce continuous oscillations.

27. In a 'slgnaling system, an oscillation circuit, a variable impedance device, means for producing ahigh frequency current in'said oscillation circuit of an amplitude substantially proportional to the impedance of said impedance device, and'a commonsource of unidirectional current conductively connect- -.ed thereto for supplying current to said means and to said impedance device 28. In a signaling system, 'a discharge tube for supplying oscillations to said systcm, a source of substantially constant current for supplying discharge current to said discharge tube, a second discharge tube, connections for also supplying said second discharge tube with discharge current from said source of current, and means to vary the impedance of said second discharge tube to produce variations in the current supplied from said source to said first tube.

29. In a signaling system, a pair of discharge tube devices having input circuits, means to independently supply carrier oscillations to the input circuit of one of said devices and signaling oscillations to the input circuit of the other,.and a common source of substantially constant current for supplying discharge current to said devices.

30. In a signaling system, an electron discharge amplifying device for supplying carrier oscillations to said system, an input circuit for said device, means for'impressing carrier oscillations upon said input circuit, a

second electron discharge device having an input circuit, means to impress signaling oscillations on said last mentioned input circuit to vary the impedance of the discharge path of said second device in accordance with said signaling oscillations, and means associating the discharge paths of said devices including means for supplying discharge current thereto and for maintaining the total .discharge current supplied. to said. two de-' vices constant as regards variations of signaling frequency.

31. In combination, an electron discharge device having a cathode, an anode, and an impedance control element, connections for supplying oscillations between said cathode and control element, a source of direct .current connected with said cathode and anode, a high inductance choke connected in series with said source, a second electron discharge device having a cathode, an anode, andan impedance control-element, said cathode and anode being connected across said source of direct current and said choke and connections independent of said first mentioned device for impressing signaling oscillations betwen the cathode and impedance control element of said second device, saidchoke offering high impedance to 'the passage therethrough of currents of signaling frequency.

32. In combination, a plurality of electron discharge, devices, each having a cathode, an anode and a control element, current supply means for supplying space current between the anodes and cathodes of said devices including means for maintaining the total space current supplied to said anodes constant as regards variations of signaling frequency, connections for causing one of said devices to generate high frequency oscillations, and mea'nsfor impressing signaling wa-ves on the circuit of another of said de-' anodes constant as regards variations of sig naling frequency and means for supplying signaling frequency potential variations to the control element of one device and potential variations of higher frequency to the control element of theother device.

34. In combination, a device for converting the energy'of direct current into high frequency oscillations. a direct-current-energy-consuming variable-impedance device, means for supplying direct current to said devices and for maintaining the total current supplied to the two devices substantially constant, and means to vary the amount of direct current energy consumed by said variable impedance device to pro.- duce corresponding variations in the direct current energy converted by said other device into high frequency oscillations.

,35. In combination, a plurality of discharge devices, each having an anode and a cathode, circuit arrangementsfor said devices including means to supply space current between said cathodes and anodes,

means to impress sustained oscillations on the circuit of one of said devices and signaling variations on the circuit of another of said devices, and means for keeping substantially constant the sum of the anodecathode currents of said devices whereby said oscil-. lations are modulated 1n accordance with said signaling variatlons.

36. In combination, two electron discharge tubes, each having a cathode, an anode, a

grid, an anode circuit and a grid circuit;

means for impressing signaling variations on the grid c1rcu1t of one tube exclusive of the other; means for impressing sustained high frequency waves on the grid circuitof the other tube exclusive of the first;

means for supplying said anodes with space current; and means associating said anode clrcuits for keeping the sum of the currents supplied to the .two anodes constant as remeans to impress signal variations on the circuit of said second tube, a path connecting said anodes capable of freely transmitting currents of signal frequency, a path' two paths and capable of freely transmitting currents of the frequencyv of said sustained oscillations.

In Witness whereof, I hereunto subscribe my name this 16th day of November: A. 1).,

" RAYMOND A. HEISING. 

